For the purpose of this application, terms presented below will be used in the manner as defined herein. “Chromatography” is a separation technique which uses differences in affinity exhibited by compounds to different materials to separate such compounds. By way of example, without limitation, compounds dissolved in a solution will exhibit different affinity for an immobile or stationary phase through which such solution is flowing. The solution is often referred to as the mobile phase. A common immobile or stationary phase is a packed bed of particles, fibers or a porous monolith held in a vessel, column, cartridge, tube, or other conical or cylindrical device or even the walls of the device.
Gas chromatography (GC) refers to solutions, mobile phases, comprised of gas. Liquid chromatography (LC) refers to solutions, mobile phases comprised of liquid. High performance liquid chromatography (HPLC) refers to methods of chromatography in which the solutions are forced through or around the stationary phase under pressure.
A material can exist as a solid, gas and liquid. A gas will become a liquid at a critical temperature and a critical pressure. A compound at such critical temperature and critical pressure is a critical fluid. However, above a critical point, a temperature above which the compound will not exist as a liquid at any pressure, compounds take on unique properties. Compounds which are at a pressure and temperature at or above the critical point are supercritical fluids. Supercritical fluids exhibit the solvation and density properties of liquids and yet have viscosity and diffusivity of gases. These properties can be modified or altered by changes in pressure, temperature or the addition of co-solvents.
The term “near critical” will be used to denote a gas compound that approaches the critical pressure and temperature which compound has substantial properties of density, viscosity and diffusivity of a critical or supercritical fluid but is below the critical pressure or temperature. For example, a near critical fluid may have approximately 5-100% of the density of the compound as a liquid but is below the critical temperature.
This application will refer to compounds as near critical fluids, critical fluids and supercritical fluids collectively as NSC Fluids.
NSC Fluids are used analytically and industrially for solvation properties. It would be useful to have methods and apparatus that couple NSC Fluid chromatography devices and methods with mass spectrometry devices and methods. Mass spectrometry methods and devices often operate at atmospheric pressure at an inlet and at high vacuum within. These large pressure differentials are complicated by the higher pressures used in NSC Fluid chromatography.